1. Field of the Invention
This invention relates to a light emitting device, and more particularly to a light emitting device which is lit whenever it is directly connected to a convenience receptacle of an AC power source or a terminal of a DC power source.
2. Description of the Related Art
Light emitting diodes (LEDs) are very popular, and are used as backup lights for electronic devices such as cellular phones, digital video cameras, personal digital assistances and so on. Light emitting diodes are also used as light emitting sources for displays, roadway signs, traffic signals and so on. In recent days, light emitting diodes are being widely applied as vehicle headlights, and ordinary lighting fixtures in place of electric bulbs and fluorescent bulbs. Usually, a battery unit serves as a power source for vehicle headlights, and supplies DC power. Generally, a battery voltage is 5 V, 6 V, 12 V, 9 V or 24 V. A commercial power source is applied to ordinary lighting fixtures, and provides AC power to them. A voltage of the AC power is 100 V, for instance.
A forward voltage Vf of the light emitting diode is 3.8 V to 3.9 V, and is lower than a voltage of the battery and a voltage of the commercial power source. Therefore, the light emitting diode is destroyed when the DC power or the commercial power is directly applied between an anode electrode and a cathode electrode of the light emitting diode.
For the foregoing reasons, the light emitting diode itself is not utilized as a lighting fixture, but is applied as a light emitting device in combination with an AC/DC power supply circuit including voltage dividing resistors and a complicated circuitry.
An example of the foregoing light emitting device is disclosed in Japanese Patent Laid Open Publication No. 2004-14899.
In the related art, the voltage dividing resistors and power supply circuit tend to increase the number of electronic components to be assembled, and lead to a complicated configuration, which means that the light emitting device becomes expensive.
The invention has been contemplated to overcome the foregoing problems, and provides a light emitting device which does not need electronic components such as voltage dividing circuits and a power supply circuit, can have a simplified configuration, and can be fabricated at a reduced cost. Further, the invention provides a light emitting device which can be directly and easily connected to a battery or a commercial power source